I believe the actual break-in period is relatively short and based on driver size and material makeup.

Interesting story. I made a few identical speakers. They were put in place one at a time as I soldered up the speaker wires to the external crossovers. I was a little impatient if excited and listened to a channel at a time as soon as possible. As each one was finished I brought them online. When they were each fired up they sounded pretty harsh next to their neighbor. There was time between each one to listen as I worked along. Each time a new one fired up it was the same. Harsh for a few minutes. A little nerve wracking. laugh

Ok. Maybe not THAT interesting. lol.